All I can remember is the trailer because I refused to watch the movie, it came out around the 2000s I believe. In the trailer there is a dude laying in his bathtub and outside it is raining. Some gross white worm or parasite makes it’s way into the bathtub and apparently turns him into this really disgusting monster who is big and bloated and can’t move, and that’s all I remember. It’s in color and in English.
Slither (2006)?
Possibly “Squirm” from 1976. Here is a link to the full movie on youtube. https://www.youtube.com/watch?v=cv5tDUiwhaQ